Anticapacity thermionic tube



Nov. 28, 1933. s MCCULLOUGH 1,937,202

ANTICAPACITY THERMIONI G TUBE Original il uly 17. 1926 IOT Patented Nov. 28, 1933 UNITED ANTIGAPA'GI-T Y' THERMIONIC- TUBE This invention relates to thermionic tiibfes and more particularly to tithesof the so ca-lled three-element type wherein there isempmyed in addition to a hot cathoda'a plate or anode and a grid or control electrode.

It has been recognized fors'ome' time that irl a tube of the ordinary three' eleinent type there is a capacity relation between the'gridbr control electrode and plate. This capacity relationis detrimental to the functioning of the tube' in" certain circuits by reason ofthe fact that it serves to effectively b'y pass a considerable 'pertion of the radio-frequency currents employed on the grid. It is also detrimental in certain circuits by reason-0f the fact that it sustains regeneration in the tube with a' consequent distortion'of signals."

Efforts have been made to overcome this capacity effect by theuse ofexternal capacities acting in cppositio'n' to the capacity e3; be tween the grid 'theplateand corriinoy re: erredto as neutr'alizing condense s, On" cnl'ty' with-the useof eateri-ial"neutralizing cuits the neut zihgba'batiitinihst be very delicately adjusted} and this adjustment is not only easily disturbed but due to th rioh' uniform ch" 'acteristicsof the tubesgmay be correct for one tube and not for ariothertubei It is, of course, impractical to vary tnis d teat-- adju's'tment every time the tube is: chang d, s0- that external neutralization i's" not universally satisfactory for this reason.- Another difiicul ty with externally neutralized circuits 'arisesfrom the capacity relation existing between different wires-that farm: the circuit, so that excessive" neutralising capacity-is intrcduce'd' into-the:cir cuit and this effectively" reduees theamplifying action of the tube. V V

The present invention proposes"sc -provide" tube wherein there is he capacity relation between the 'gridand the plate'so that externai neutrali= zation need not be resorted to. I a

The atu e of the resent invention may be readily understood by reference to the aecofii:

panying drawing which illustrates one enibbdi ment of my invention and in which: Figure l is sung-ram of the tube; Figure 2 represents a transverse vertical section through an assembled tube;

Figure 3 is a similar section at right angles to Figure 2, the enclosing envelope not being shown in this figure;

Figure e is a section in the plane of line IV-IV of Figure 2.

' element will tend to des'troy' the capacity rel the tube will have an envelope 13 infwhich"ist e igure-'5 1 is" a vertical section Sh'bWi'ii'g the grid and aiitic'apacity'element-iii el'va'tin, ans;

The 'natiire of' theinventien 'may be g nerazi descr bed in- -cofinetioii with; the diagram shewn V am; dicatesatubewh h has -roar' ccntaet pin ine basetherenft'o conforr'n te'stafidardpre ti'ce-Q The-first ping nilfilbi" 2 ,leadsdirectly'to tfie gri PiiEQ-afidfibfifibt the' ca-thedeor filaffiht 6. Phi? cbilnct to the mid-point of a coil 8 built intof thef-tule s'tl'lifstlife one eta 9 o f'jtlie coil =ScGnfiBEts With tlie' pl'ate or aiiodeIO-L The-other ens 1150f coil connects with an anti capaizity eleinefit -2 builtintthe =ti1be stiilture aiifi beaiffil' "1711 S8,- relatiori to tlfe"plate lothatthigi'id3*has: grid-"san the anti ea acity eminiifiiaeat are of a prbszimatay" the s'tfnelength ahdi'hfltbilfi? stantiall'y tire-same surface are Eacl'r or tli 111' is disposed "the seine distance froifi the" plateafid the positions or each wnh' respect te tfi plate aisfibstal' ltiatly identieal Neither is" carer to t platethan the other and they bet cu'py stantiallythesamepiisitioii irrthe tub the cathode" ana the} plate} The In'i fibef12 preferably-isceatfi wit F sitant insifiation so as to rfiiri'l T the g at? e'st possible extent any new" of current-between it andthence-filament, Z V

It will be apparent to thds'sk'illd in that "since the plate 10am the anti-cabs mentm are at apposite-master Wlhdi' andsince this winding "8 is tapped-at as midthat, whilebdth the plate and the ahtl-dbac eleinen't will have a pes'itive-'potential' with? ef i erene'e to the-"direct currentapplied to the a'n'o e in the usual manner, the anti-capacity element win-nave a'potential u pcsiteta thatofth mad 10" with referenceto' raaioere'qe'eney osc atio" '195 inthe tube cirdlil't. Frequently the anti-cap can existing between 1 the grid' Bandthe h therebyprovidin'g ari'inte'rnall-y'nutraliz '5 In 'tne ractiearembodiment "0f the inventiom;

usii'alstein 14am whichis secured, intheusiialmanner, in a base 15. The pins 2, 4, 5 and '7 are arranged. in the base 15 in accordance with the usual practice. The filament 6 is supported in the tube in accordance with present practice,

being carried on wires 6a and 6b which pass through the stem 14. The grid 3 and anti-capacity element 12 are carried around spaced apart parallel porcelain or other refractory non-conducting rods 16. The rods 16 are supported on wires 17 and 18 which pass through the stem 14. Wrapped about the rods 16 in parallel relation are wires 3 and 12 providing the grid and the anti-capacity elements respectively. The rods 16 are preferably notched or grooved to retain the wires in proper spaced relation out of contact with each other. For the purpose of illustration, I have indicated the cross-section of the grid wire 3 as an open section and the cross-section of the anti-capacity wire 12, which is insulated in solid black. This is for the purpose of convenience. The rods 16, which preferably have openings extending therethroughare braced at the top by an inverted U-shaped wire 19, the legs or" this wire extending down into the rods but being separated from the upper ends of the respective wires 17 and V 18. Thegrid 3 is connected with the wire 1'7 and the anti-capacity element 12 is connected with the wire 18. The plate 10 is in the form of a flat sheet at each side of the structure formed by the two rods 16 and the associated elements 3 and 12 and is carried on a wire 20 passing through the stem of the envelope. It will be seen that fila- 1 ment 6 is inside the cage provided by the wires 7 3 and 12 and the supporting rods 16. The plate 10 is equally spaced from the wires 3 and 12 and these wires occupy substantially the same relative position between the filament and the plate. The surface areas of both wires are the same, so that neither has a capacity effect greater than the other.

Inside the base 15 and below the envelope is an inductance coil 8. This coil may be disposed around the lead wires through the base in such manner as not to interfere with the assembly of the tube and can be of such a size as will give the best results in the use. The plate lead wire 20 connects to one side of this coil while the pin 7 in the base connects to an intermediate point thereof. The lead wire 18 connecting to the anticapacity element; 12 is in circuit with the other end of this coil, in accordance with the diagram shown in Figure 1.

.The operation of the tube is in substantially all respects similar to the operation of the ordinary three-element tube, the chief difference being that the anti-capacity element-12 serves to eliminate any capacity effect between the grid and the plate. This reduces the tendency of the tube to oscillate and makes it particularly useful in amplification circuits, especially circuits for effecting amplifications for radio-frequency circuits. By reason of the anti-capacity element-l2 being coated with an insulating material, it will not actively function as an electrode to divert the electron current between the plate and the oathode.

.Since the capacity effect between the grid and the plate is eliminated, there is no need for external neutralization of the circuit in which the tube is employed, and the characteristics of the circuit will not be materially chan ed by the substitution of one tube for another. In many circuits where an attempt is made foo-neutralize the internal capacity of v the tube by an external means, the circuit is made unstable by the substitution of one tube for another, thereby introducing practical difiiculties into this method of avoiding internal capacity effects.

The manufacture of the tube can be accomplished in accordance with present methods and the tube degasified in the usual manner.

In the form of tube shown in Figures 5 and 6, the same reference numerals designate corresponding parts, except that the reference numerals have a prime mark applied thereto. In this form the anticapacity element 12 is disposed outside the grid and adjacent thereto, and is formed of vertically arranged insulated wires.

While I have illustrated a specific embodiment of my invention, it will be understood that this is merely by way of illustration, and I do not limit myself to the particular construction and arrangement shown, as the invention may be otherwise embodied within the contemplation of my invention.

I claim:

1. A thermionictube having a cathode, a plate, a grid, and an anti-capacity member in the tube, an inductance in the base of the tube having one end connected to the anti-capacity element and having its other end connected with the plate, and a central tap for the inductance.

2. An electron tube having a cathode, an anode, and a grid, an anti-capacity member in the tube in proximity to the grid, and an inductance connecting the plate and the anti-capacity memher, said inductance having a central connection therein through which a direct current potential may be applied to the anode.

3. A thermionic tube including an envelope, a base for the envelope, a cathode, a plate, a grid, and an anti-capacity element, said cathode, plate, grid, and anti-capacity element being within the envelope, and an inductance in the base outside the envelope, said inductance being connected at one end to the anti-capacity element and being connected at its other end to the plate and a terminal in the base connected to an intermediate point of the inductance, said base also having contact terminals leading to the cathode and the grid.

4. A thermionic tube having therein aplate, a cathode, a grid, and an anti-capacity element having insulation thereon, saidplate and anticapacity element being connected in out-of-phase relation with each other.

5. A thermionic tube mount including a grid supporting element comprising a post formed of insulating material and having a plurality of notches therein, and a wire entered in one end of the post and supported by the tube for holding the post in a fixed position. a

6. A grid structure for thermionic tubes comprising a plurality of parallel posts of insulating material having a series of peripheral notches therein, and a pair of conductors wrapped about and supported by the posts, the wires setting'in the notches and being maintained in spaced relation thereby, one of said conductors constituting a grid and the other a shielding electrode.

' FREDERICK s. McCULLOUGI-I. 

